6Physiology of the bladder functionThe bladder stretches as it fills with urine and when there is 250mL you feel the need to void.Voiding begins with voluntary relaxation of the external urethral sphincter muscle.Once you relax the urethral sphincter the involuntary response of contraction takes over. AKA micturitionInability to void because kidneys are not excreting urine is known as suppression.Inability to void even though urine is present in the bladder is known as retention.Involuntary micturition = Incontinance

7UrethraSmall tube lined with mucous membrane leading from the floor of the bladder to the exterior of the body.In females this distance is about 3cm.In males this distance extends along a winding path for about 20 cm and passes through the middle of the prostate gland just after leaving the bladder. & is shared as part of the reproductive system.

8Microscopic Structure of the functional unit of a kidney is the Nephron.Components of the NephronBowman’s CapsuleProximal convoluted tubuleLoop of HenleDistal convoluted tubuleCollecting ductThere are approximately1.25 million nephronsPer Kidney.

12The collecting ducts empty into the calyces which empty into the renal pelvis.

13Blood vessels of the KidneysAbout 1200 ml of blood flows through the kidneys every minuteWhich means approximately 1/5 of all the blood pumped by the heart per minute goes to the kidneys.Usual direction of blood flow isArteries-Arterioles-Capillaries-venules-veins

15Function of the kidney KIDNEYS…Process blood plasma and excrete urine.Most important organs in the body for maintaining fluid-electrolyte and acid-base balances.Excrete Nitrogenous wastes from protein metabolism. (urea)

17Kidneys also… Influence the rate of secretion of the hormonesADH – Antidiuretic hormoneAldosteroneand synthesize erythropoietin –active form of vitamin D and prostaglandins.

18Urine is formed by 3 meansFormation of urineUrine is formed by 3 means1. Filtration – the movement of water and solutes from the plasma in the glomerulus, across the glomerular-capsular membrane, and into the capsular space of the Bowman’s capsule

192. Reabsorption- movement of molecules out of the tubule and into the peritubular blood.

203. Secretion – movement of the molecules out of the peritubular blood into the tubule for excretion.

21FiltrationOccurs through the glomerular capiliaries to the Bowman’s CapsuleLarge substances are separated from small substances.Blood cells and blood proteins are typically TOO large to filter through the glomerulus so as the blood leaves the glomerulus in the efferent arteriole it is relatively clean and has lost most of its fluid.

22Blood cells are too large to filter out. So what does filter out?WaterSaltsBicarbonateH+UreaGlucoseAmino acidsSome drugs

23Returned to the blood immediately: Reabsorption occurs mostly in the PCT.Water and ionsGlucose and amino acidsPassive and Active transport mechanisms are at work in the tubules.MANY Carriers are available for materials that need to be reclaimed.Very few carriers for things that are of little or no use to the body.

24Reabsorption in Reverse: SecretionAnd it gets rid of substances not already in the filtrate such as drugs.H+ and K+ and creatinine move from the peritubular blood to the tubule.

25Urine vs. FiltrateFiltrate contains everything that blood plasma does (except proteins)Most of the Water, nutrients and necessary ions are reabsorbed by the time it reaches the collecting ducts.Urine contains most of the waste and unneeded substances.

26In 24 hours150 to 180 liters of blood plasma filter through the kidneys (nephrons)Only 1 to 1.8 liters of urine are produced.WHAT HAPPENS TO MOST OF THE FILTRATE?Initial Filtrate –diluteFinal Filtrate - concentrated

28Balance of Water and electrolytesWe cannot lose more water than we take in.Water is lost by….Respiration, Perspiration, Solid waste, & UrineWater is taken inin Foods, beverages and metabolism.

29Electrolyte balanceADH – prevents excess water loss by causing the collecting duct cells to reabsorb more water which increases blood volume and blood pressure.Alcohol disrupts ADH and less water is reabsorbed creating more dilute urine.If ADH is not present up to 25 liters /day could by flushed from the body.= severe dehydration.